Overview of By-products in Meat Processing Plants

When a meat processing plant produces the cuts of beef, pork, or poultry that consumers take home, it also generates a substantial stream of materials beyond the primary product. Research published in PMC notes that by-products of cattle, pigs, and lambs can account for 66%, 52%, and 68% of live weight respectively – meaning the primary meat cut is, in many cases, the smaller fraction of what comes off the animal. Managing this enormous volume of material is not an afterthought; it is a central pillar of operational efficiency, profitability, and environmental responsibility in any meat processing facility.

What counts as a meat plant by-product? 🔗

The term “by-product” covers a wide range of materials generated at different stages of slaughter and processing. A review in Meat Science describes these as large amounts of co-products requiring rational management for ecological disposal. In practical terms, they fall into three broad groups.

Edible by-products include organ meats – liver, heart, kidneys, tongue, and tripe – which are consumed directly in many cuisines globally and carry significant nutritional value. Inedible by-products encompass bones, hides, hooves, horns, and blood. Processing by-products are the fat trimmings, meat scraps, and connective tissues removed during the production of finished products like sausages, kebabs, hot dogs, and deli meats.

In the United States, the meat-packing industry considers everything produced from the animal – except dressed meat – to be a by-product, with edible and inedible classes handled under separate regulatory frameworks. The USDA-FSIS further specifies that meat by-products used in sausage formulations must be listed in the ingredient statement, giving regulators and consumers full visibility.

Rendering: the core process for converting by-products 🔗

The most important industrial process for turning raw by-products into stable, usable materials is rendering. According to Wikipedia’s entry on rendering, the process simultaneously dries the raw material and separates fat from bone and protein, yielding a fat commodity and a protein meal. This single process is responsible for transforming what would otherwise be waste into commodities traded on international markets.

Dry rendering vs. wet rendering 🔗

In dry rendering, ground material is heated in a steam-jacketed vessel to drive off moisture and release fat. The solids left after fat drainage – called “cracklings” – are ground into meat and bone meal. In wet rendering, the material is cooked with added steam and then pressed; the water-fat mixture is separated by centrifuging, and the remaining solids are dried and milled. Edible rendering, carried out at lower temperatures by meat processing companies themselves, is used for fat trimmings destined for food-grade applications like lard and edible tallow.

What rendering produces 🔗

The two main outputs of rendering are fat products and protein meals. On the fat side, tallow and grease are widely used in soap, candles, cosmetics, lubricants, biodiesel, and as animal feed ingredients. High-quality tallow from beef fat trimmings can enter cosmetic and food-grade supply chains, while lower grades are directed to industrial and biodiesel applications. On the protein side, the solids are dried and ground into meat and bone meal (MBM) or meat meal, which are concentrated sources of protein, calcium, and phosphorus for animal feeds.

Fat trimmings and their value chain 🔗

Fat trimmings are generated at every stage – from initial carcass dressing through the production of value-added products like sausages and kebabs. Friesla, a meat processing systems company, notes that tallow is having a significant moment commercially, with growing demand from both industrial buyers and artisanal food producers. Fat trimmings from sausage production lines can be consolidated with other fat streams and rendered together, making this a logistics-efficient material to manage.

The grading of tallow matters commercially. Food-grade tallow rendered from inspected, edible fat under USDA oversight can be used in cooking and food manufacturing. Industrial-grade tallow goes to soap-making, candle production, and the steel rolling industry – where, as noted in the context of steel manufacturing, tallow provides lubrication during sheet compression. The diversity of end markets means fat trimmings rarely go to waste when managed well.

Bones: from fresh sales to bone meal 🔗

Bones are among the most commercially flexible by-products in a meat plant. Fresh, whole bones – especially marrow and soup bones – can be sold directly as value-added products to retailers or pet food manufacturers. Processors are increasingly marketing cut bones directly to dog owners and raw-feeding pet food brands, which generates a premium above what rendering would return.

Bones not sold fresh are processed into bone meal through cooking and grinding. ScienceDirect’s overview of meat and bone meal describes it as a dried mammalian tissue product with approximately 50% protein and 8-10% fat, and a calcium content of 8.8-12%. This profile makes it an effective calcium and phosphorus supplement in livestock and poultry diets.

The Poultry Extension resource at poultry.extension.org confirms that slaughter by-products, once rendered, serve as nutritionally valuable and economical feed ingredients – covering meat trimmings, inedible parts, and organs. The protein quality and mineral density of MBM make it a standard ingredient in commercial poultry and swine rations.

One important regulatory caveat: feeding MBM to ruminant animals has been restricted or banned in most parts of the world following its link to bovine spongiform encephalopathy (BSE, or mad cow disease). It remains permitted for monogastric species such as pigs, poultry, and fish, and is widely used in dog and cat food in the United States and elsewhere.

Meat scraps and the pet food industry 🔗

Lean meat scraps – the small offcuts that accumulate throughout cutting and trimming operations – are too small to package as retail cuts but are nutritionally intact. The American Association of Feed Control Officials (AAFCO) defines meat by-products as clean, non-rendered parts other than skeletal muscle meat, including organs, blood, and bone. These materials form the nutritional backbone of large portions of the commercial pet food market.

Rendered pet food ingredients make up 40 to 60% of most finished kibble formulations for cats and dogs. Rendered meat scraps appear on pet food labels as “meal” ingredients – chicken meal, lamb meal, and so on – which are more concentrated in protein per unit weight than fresh meat because moisture has been removed. This makes them a cost-effective and nutritionally dense option for pet food formulators.

The pet food channel is a significant revenue driver. The ScienceDirect review on meat by-product sustainability highlights that protein hydrolysis of by-products generates bioactive peptides with relevant physiological effects, creating premium ingredient opportunities for the pet food, pharmaceutical, and cosmetics industries – far beyond standard meal production.

By-products from value-added meat products: sausages and kebabs 🔗

When a plant produces further-processed products – sausages, kebabs, hot dogs, deli meats – it generates a secondary tier of by-products from the shaping and formulating process itself. These are distinct from primary slaughter by-products and require their own management systems.

Research in the journal Meat and Muscle Biology points out that whole cuts are sold at a premium while portions left over from trimming, shredding, and cutting are repurposed as sausages, burgers, and similar comminuted products. This cascading utilization model ensures that value is extracted at multiple levels of the production chain.

FAO’s small-scale sausage production guidance illustrates this directly in sausage formulation: fat trimmings and fatty tissues are reduced through grinder plates at specific sizes, then blended with lean meat, curing salts, and spices. The University of Georgia’s extension service similarly describes sausage making as a purposeful way to use nutritious trimmings from beef, pork, lamb, and game meats, reducing waste while creating a value-added product with established market demand.

Lean meat scraps from sausage and kebab production that are too small even for comminuted products can be further processed into meat pastes for canned products, or consolidated into the pet food ingredient stream. Meat restructuring technology also enables low-value carcass cuts and trimmings to be reformed into structured products like formed patties and slices – extending the value chain even further through physical, chemical, and enzymatic processing techniques.

Economic and environmental significance of by-product management 🔗

Efficient by-product utilization is not only an environmental obligation – it directly affects whether a meat processing plant is profitable. According to a PMC review on meat by-product utilization, approximately 11.4% of gross income from beef and 7.5% from pork come directly from by-products. For many smaller operations, this income stream determines whether the business breaks even.

The ScienceDirect sustainability review emphasizes that efficient solutions are critical for the meat industry’s transition to a bioeconomy – where inedible fats are converted to biodiesel, proteins are hydrolyzed into functional food and pharmaceutical ingredients, and collagen is extracted for gelatin and cosmetic applications. Research published via Springer further confirms that animal by-products and wastes are a viable source of renewable energy, and that their economic utilization is feasible at commercial scale.

On the environmental side, the same Springer review cautions that slaughterhouse wastewater carries high fat, grease, and protein content, and that unmanaged animal waste creates biological contamination risks and pest attraction. Proper processing – whether through rendering, composting, or direct sale – converts this liability into a controlled, often profitable output stream.

Market dynamics add another layer of complexity. Tallow prices respond to biodiesel demand cycles, while bone meal prices track feed ingredient markets. Plants that monitor these commodity markets and adjust their by-product processing strategies accordingly gain a meaningful competitive advantage, particularly in markets where demand for sustainable, traceable leather and high-quality raw pet food ingredients is growing.

Regulatory frameworks governing by-product use 🔗

By-product processing operates under strict regulatory oversight in most countries. In the United States, all meat processing facilities have been required since 2000 to maintain both a written sanitation program and a HACCP (Hazard Analysis and Critical Control Points) program, which governs how by-products are handled, stored, and directed to their downstream uses. The USDA-FSIS requires that meat by-products used in processed products such as sausages be fully declared on ingredient labels. In Europe, category-based classifications determine which by-products are permitted in which applications – with Category 3 materials (from animals inspected and passed as fit for human consumption) being the only stream permitted for inclusion in animal feed and pet food.

State and federal regulations in the US also govern specific practices such as the mandatory discard of beef heads from cattle over 30 months of age, the cleaning requirements for intestinal casings, and the bleaching of pork tripe before sale. These rules ensure food safety at every step of the by-product value chain.

What do you think? Given that by-products can account for more than 10% of a meat plant’s revenue, how central should by-product strategy be in the operational planning of a new processing facility? And as consumer interest in sustainable sourcing grows, do you think transparency about the use of meat plant by-products in pet food and animal feed will become a competitive advantage rather than a liability?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC3614052/
2. https://www.sciencedirect.com/science/article/pii/S0309174021001844
3. https://en.wikipedia.org/wiki/Meat-packing_industry
4. https://www.fsis.usda.gov/sites/default/files/media_file/2021-03/FPLIC_4a_Sausage_Operations.pdf
5. https://en.wikipedia.org/wiki/Rendering_(animal_products)
6. https://www.sunriserendering.com/meat-rendering-understanding-the-process-and-its-uses/
7. https://friesla.com/blog/creating-value-added-products-meat-processing-waste/
8. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/meat-and-bone-meal
9. https://poultry.extension.org/articles/feeds-and-feeding-of-poultry/feed-ingredients-for-poultry/animal-by-products-in-poultry-feeds/meat-and-bone-meal-in-poultry-diets/
10. https://en.wikipedia.org/wiki/Meat_and_bone_meal
11. https://www.feedingravendoodles.com/articles/by-products-and-meat-meal
12. https://truthaboutpetfood.com/almost-everything-about-rendered-pet-food-ingredients/
13. https://www.sciencedirect.com/article/pii/S0309174021001844
14. https://www.sciencedirect.com/article/abs/pii/S2214799322001400
15. https://www.fao.org/4/x6556e/x6556e07.htm
16. https://fieldreport.caes.uga.edu/publications/B1437/basics-of-sausage-making-formulation-processing-and-safety/
17. https://www.tandfonline.com/doi/full/10.1080/19476330903010193
18. https://link.springer.com/chapter/10.1007/978-981-15-8967-6_11
19. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/meat-processing